As a representative of the third generation of semiconductor materials, gallium nitride (GaN) has many excellent characteristics, such as high critical electric field for breakdown, high electron mobility, high two-dimensional electron gas concentration, and good high temperature working ability, etc. The third generation of semiconductor devices based on gallium nitride, such as high electron mobility transistor (HEMT), heterostructure field effect transistor (HFET) and the like, have been put into use, and have obvious advantages especially in areas requiring high power and high frequency such as radio frequency and microwave, etc.
GaN HEMT is mainly used in the communication industry and power electronics industry, but it also has unique advantages in the field of high-speed digital circuits and mixed signals. GaN HEMT has excellent high temperature stability and can greatly reduce the cost of the circuit in terms of heat source and temperature field control. The wide bandgap characteristics of GaN enable it to have both high electron saturation speed and high breakdown voltage, allowing a device to operate at higher voltages, which can improve the driving capability of the circuit. Therefore, compared with the traditional silicon-based technology, digital circuits based on GaN HEMT can meet the requirements of operating under large current and voltage swings and in harsh environments, making it potentially of great application in corresponding fields.
In order to realize GaN HEMT-based digital circuits, it is necessary to realize monolithic integration of high-performance GaN-based E/D HEMT. Compared with conventional D-mode (depletion mode) GaN HEMT, the E-mode (enhancement mode) GaN HEMT is relatively difficult to manufacture. However, the E-mod GaN HEMT is not only required to realize DCFL logic (Direct-Coupled FET Logic), but also its performance plays a crucial role in the characteristics of the circuit. Therefore, on the basis that the E-mod GaN HEMT is difficult to manufacture, it is even more difficult to realize the monolithic integration of E/D mode HEMT.